Extrusion and Alkali Extrusion of Corn Stover to Improve Enzyme Saccharification

Pretreatment of biomass before subjecting it to enzyme saccharification is crucial with regards to facilitating access of enzyme to biomass. Extrusion, as a continuous and cost-effective pretreatment method, combines heating with high shear and mixing resulting in much greater specific surface areas of biomass. The objective of this study was to examine the effect of extrusion as a pretreatment method and the underlying factors that impact the improvement of sugar yields. The optimum glucose and xylose sugar recoveries were 48.79% and 24.98%, respectively, at 27.5% moisture content and 80 rpm screw speed. These yields were 2.2 and 6.6 times higher than those for untreated corn stover. X-ray diffraction (XRD) analysis showed that crystallinity index was not a good indicator of sugar yield. However, scanning electron microscopy (SEM) showed that cellulose network was exposed due to destruction of the lignin sheath. Langmuir adsorption model was shown to be an effective tool for estimation of specific surface area (SSA) of corn stover. The SSA of pretreated samples were significantly amplified over the control revealing that extrusion can open the cell wall at microscopic scale which was especially favorable on sugar yields. INTRODUCTION Renewable energy, including ethanol, was not given enough attention until the eruption of the “oil crisis” in the 1970s. The price advantage of fossil fuel was impaired and spurred multiple explorations such as National Alcohol Program in